This is where entities like the FAA come into play — deciding conclusively what's safe airspace, and what's not. And it's not just America that has an overseeing group to keep the skies safe and secure: Europe has one too, called Eurocontrol, which has a similar airspace ban over Ukraine in place.

With Israel now off-limits until at least Wednesday, it does raise an obvious question — how dangerous is too dangerous for the FAA? There are certainly countries in the world that the U.S. could consider hostile, either by their governments, or sentiments from some of their citizens. What makes one too dangerous to fly over, and another a fair risk? Well, here are some places the FAA prohibits or limits U.S. airlines from flying over, for example.

1. Iraq

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Predictably, the country of Iraq isn't considered a prime fly-over route for the FAA. Although you can actually pass over Iraq, concerns about attacks by militants spurred the FAA to place a hard altitude limit on such flights. No U.S. plane is allowed to pass through Iraq at an altitude of 20,000 feet or below, whether commercial or not, due to fears of an event like what happened in Ukraine.

2. North Korea

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This one definitely makes sense. North Korea is infamous for launching ballistic missiles without particular warning or provocation, ostensibly to test their capabilities. The country is likely the world's most isolated dictatorship, and as such, there's not exactly a lot of coordination going on with international aviation authorities. This is a combination of factors that makes the call for the FAA pretty easy — the skies over North Korea are a no-go area.

3. Libya

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Under the oppressive rule of the late Colonel Muammar Gaddafi just three years ago, the revolution in Libya hasn't made it intrinsically safer for Americans. While it's easy to forget what the word "Benghazi" means when it's typed in all-caps over and over again on message boards, it's actually Libya's second largest city, where ambassador Chris Stevens was slain in a terrorist attack in September 2012.

As MarketWatch observes, the country is quite weaponized in the aftermath of the Gaddafi government's downfall — the likelihood of anti-aircraft guns being present amongst the general population was enough for the FAA to say no way. The State Department, as well, has urged Americans not to visit Libya, and to leave if they're there, citing security concerns that leave their embassy with "very limited emergency services" for U.S. citizens.

4. Eastern Ukraine

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Well, no surprises here — U.S. airlines aren't allowed to fly over Eastern Ukraine anymore, thanks to the shooting down of MH17. This was actually an expansion of an existing restriction which barred flights from cruising over the skies of Crimea after the peninsula was annexed by Russia in April.

The crash of MH17 was a wake-up call about the dangers of the region. Now, the FAA has expanded the restriction, banning flights from entering airspace over Eastern Ukraine, as well. Like the bans on flight over Libya and North Korea, this one is absolute — no U.S. flights over Eastern Ukraine, no matter the altitude.